The Biostatistics Core Facility (BCF) of the University of Chicago Comprehensive Cancer Center (UCCCC) provides collaborative statistical support to UCCCC investigators engaged in clinical, basic, and population science research. The Facility is currently staffed by five PhD statisticians, two masters level biostatisticians, and one research programmer in addition to the Scientific and Technical Directors. The services provided by the BCF include collaboration in the formation of study designs and data analysis plans; protocol development, randomization, and statistical analysis for Phase 1, Phase 11, and Phase 111 clinical trials; assistance in the design and analysis of retrospective and prospective observational studies; and statistical collaboration on basic science and animal research projects. Clarification of specific aims and hypotheses to be tested, specification of primary and secondary outcome variables, sample-size (power) calculations, and development of data analysis plans are major areas of activity during the study design phase, followed by statistical analysis and assistance in the preparation of manuscripts for publication after completion of data collection. The BCF also interacts closely with the Cancer Clinical Trials Office and the UCCCC IT group on database development and data management procedures to ensure a high level of data quality for clinical trials and other studies conducted within the UCCCC, as well as the newly developing Bioinformatics Core to support investigators engaged in bioinformatics research and other high-dimensional data problems. BCF members also serve on two key UCCCC committees, namely, the Clinical Trials Review Committee and the Scientific and Accrual Monitoring Committee, thereby ensuring that all protocols and cancer-related research projects undergo rigorous biostatistical review and that patient accrual to ongoing studies is proceeding at an adequate rate. Finally, BCF members participate in teaching activities, and conduct statistical methodological research in support of projects conducted within the UCCCC.